The present invention relates to a method and a system for monitoring a person. In particular the present invention relates to a method and a system for monitoring drowsiness of a person performing a task where it is important to be awake, such as a person driving a car, monitoring personnel in a nuclear power plant or in a radar office, or a pilot.
In today""s traffic, there is a problem relating to people driving vehicles despite the fact that they are too tired, sleepy or drowsy in order to safely drive their vehicle. In particular, during longer journeys, a person may start the journey in good shape and then as times goes being more and more drowsy, and, in the worst case, finally go to sleep. Such a scenario is of course highly undesirable, since it poses a great threat to both the driver and persons around him/her, such as other drivers or passengers in vehicles on the same road.
Also, it is known that when a person becomes drowsy, the eyelid and pupil movement pattern changes. Furthermore, in WO/33403 a method where the corresponding relationship between cardiac and respiratory functions are used in order to detect a condition of drowsiness.
It is an object of the present invention to provide a method and a system, which have an improved reliability over the prior art. It is also an object of the present invention to provide a method and a system, which is more robust and user friendly compared to the methods according to the prior art.
This object is obtained by means of monitoring the autonomic nervous system, and in particular parameters reflecting the current condition of the autonomic nervous system. Thus, by means of intensive research it has been possible to show that it is in fact a change in state in the autonomic nervous system that causes the body to change certain patterns in, for example, eye movements. Thus, changes in activities in the autonomic nervous system are reflected by changes in behaviour of certain physiological parameters.
In a preferred embodiment the method and system comprise continuous recording of at least one parameter reflecting the current state of the autonomic nervous system, such as a parameter reflecting cardiac activity. If a trend in the monitored parameter fulfils a certain criteria or certain conditions, such as slowing down of the activity, a first alarm level is triggered by the system. At the first alarm level a second parameter reflecting the autonomic nervous system can be monitored in addition of the first parameter, such as body motor activity or respiratory activity. If both the monitored parameters exceed a pre-set threshold value an alarm is generated indicating that there is a risk that the person may fall to sleep. In this manner a multi-step threshold model is formed, which is used to indicate a potential risk of falling asleep.
When such an alarm is generated a number of different actions can be taken. For example, a light or sound signal can be generated, an air puff, or another change in the physical environment, or a vibrator located in the seat where the person is seated can be activated.
The invention relics on the fact that extensive studies have shown that the autonomic nervous system reflects the wakefulness level of a person. Thus, by monitoring a parameter, which reflects the current state of the autonomic nervous system, a lower level of wakefulness can be detected. One such parameter, which has been found to indicate such a state, is cardiac oscillation. Thus, the autonomic nervous system affect the heartbeat of a person falling to sleep in such a way that the heartbeat will go through a series of acceleration and de-acceleration.